In photography, there is often a need to adjust brightness of different parts of an image. For example, consider an image captured in the midday sun. If an exposure is selected so that brightly lit objects are accurately captured, shadowed objects will be very dark and lack detail. On the other hand, if an exposure is selected so that shadowed objects are accurately captured, the brightly lit objects will appear washed out.
Traditionally, this problem has been solved with a “fill flash” technique. A flash unit illuminates areas that would otherwise be in shadow. One disadvantage of using a fill flash is that it requires knowledge and training that is beyond what many amateur photographers possess. Another disadvantage is that it requires a flash attachment for the camera.
In conventional film photography, this problem has also been solved with dark room techniques, such as “dodging” an area of a print to make it lighter or “burning” an area of a print to make it darker. However, the traditional dodging and burning techniques are not available to digital photographers.
In digital photography, special purpose digital photo manipulation software running on a personal computer can be used to manipulate a digital image. For the casual photographer this approach has several disadvantages. The software is expensive, requires powerful hardware, and requires a substantial investment of time to learn how to use the software. Moreover, the casual photographer is accustomed to seeing a captured image immediately. With special purpose photo manipulation software, there is a significant time delay before the corrected image may be seen.
Accordingly, there is a need for methods and apparatus for generating a digital image in which exposure varies by region of the image.